Various zinc dialkyldithiophosphates (ZDDP) are known as very effective anti-wear, anti-oxidant additives. These compounds have been used as additives for lubricating oils since the early 1940s. However, due to their phosphorus contents, the addition of ZDDPs to motor oils adversely affects the catalytic efficiency of exhaust emission catalytic converters which are installed nowadays in most cars to reduce pollutants in the exhaust gas. In addition, metallic ZDDPs can cause ash formation and have antagonistic interactions with dispersants which are normally added to lubricants. Thus, non-metallic, ashless anti-wear/anti-oxidant products which can replace ZDDPs as additives to lubricants will have a lesser tendency to produce sludge.
A number of dithiocarbamate derivatives have been known to be useful as lubricant additives (e.g., U.S. Pat. No. 3,890,363; U.S. Pat. No. 3,833,496; U.S. Pat. No. 4,440,676; U.S. Pat. No. 4,502,972; U.S. Pat. No. 4,795,684; U.S. Pat. No. 4,758,362; U.S. Pat. No. 4,125,479; U.S. Pat. No. 3,856,836; U.S. Pat. No. 3,342,835; U.S. Pat. No. 4,400,298; U.S. Pat. No. 3,462,368; U.S. Pat. No. 3,412,026; EP Patent No. 211,806; EP Patent No. 285,455; EP Patent No. 220,136; and W.O. Patent No. 87/05622).
A significant number of borate esters of mono- and di-hydroxy derivatives have also been known as has their use as lubricant additives (e.g., U.S. Pat. No. 4,486,323; U.S. Pat. No. 4,486,321; U.S. Pat. No. 4,273,665; U.S. Pat. No. 4,374,032; U.S. Pat. No. 4,376,712; U.S. Pat. No. 4,382,006; U.S. Pat. No. 4,328,113; U.S. Pat. No. 4,410,436; U.S. Pat. No. 4,447,560; U.S. Pat. No. 4,507,216; U.S. Pat. No. 4,400,284; U.S. Pat. No. 4,440,656; EP Patent No. 36,708; EP Patent No. 285,455; EP Patent No. 220,136; and German Offen. No. 3,327,859).
Therefore, due to environmental concerns, there is a need for specially formulated lubricants which contain no phosphorus or only a very low concentration of phosphorus.